NGSS HS-LS2-2: Biodiversity & Population Dynamics

Estimated Time: 45-60 minutes Materials: Computer with internet access, Biodiversity & Population Dynamics Simulator, graphing paper (optional).

Part 1: Engage (Anchoring Phenomenon)

A local wetland historically supported a high population of wading birds and diverse fish species. Over a ten-year period, a new factory was built nearby, slightly increasing pollution, and a new predator species was introduced. At first, the ecosystem seemed fine. However, after an unexpected, moderate drought (a disturbance), the ecosystem crashed completely and never recovered, while a similar wetland nearby survived a similar drought easily.

Question: Why do some ecosystems withstand sudden disturbances while others collapse? What factors control the underlying resilience and “carrying capacity” of an ecosystem before a disaster even hits? Write down your initial ideas below. ___ _______

Part 2: Explore (Simulation Investigation)

Open the Biodiversity and Population Dynamics simulation. This model allows you to change the Ecosystem Scale, Habitat Area, and various bottom-up (resources like water) and top-down (stressors like predation, pollution, and climate) factors over a 30-year period.

Activity A: Baseline and Bottom-Up Factors

1. Set the Ecosystem Scale to “Regional Forest” and Habitat Area to 500 km².
2. Set Pollution, Climate Stress, Invasive Species, and Predation Pressure to 0%.
3. Set Water Availability to 50%.
4. Click Run 30-Year Model. Record the final Population, Biodiversity Index, and Estimated Carrying Capacity (K) in the data table.
5. Change Water Availability to 10% and re-run. Then change it to 90% and re-run. Record all data.

Activity B: Top-Down Factors and Stressors

1. Return Water Availability to 50%.
2. Change Pollution to 80% (leave others at 0%). Run the model and record (Scenario 4).
3. Reset Pollution to 0%, change Predation Pressure to 80%. Run the model and record (Scenario 5).

Activity C: Disturbances and Resilience

1. Set up a Resilient Ecosystem: Water Availability 100%, all stressors (Pollution, Climate, Invasive, Predation) at 10%. Run the model. Then click Trigger Disturbance and record the new final Population and Biodiversity.
2. Set up a Stressed Ecosystem: Water Availability 50%, all stressors at 50%. Run the model. Then click Trigger Disturbance and record the new final Population and Biodiversity.

Part 3: Explain (Sensemaking)

1. Mathematical Representation: Look at your data for Scenarios 1, 2, and 3. How does the bottom-up factor (Water Availability) mathematically relate to the Estimated Carrying Capacity (K)? Does K increase, decrease, or stay the same when water decreases? ___ _______

2. Comparing Factors: Compare Scenario 4 (High Pollution) and Scenario 5 (High Predation). Did both affect the final population? Did they both affect the Biodiversity Index equally? Explain using your data. ___ _______

Part 4: Elaborate / Evaluate (Argumentation & Revision)

The Task: Look back at your initial explanation in Part 1 regarding why the wetland ecosystem collapsed after a drought. Use the mathematical representations (the graph trends and final output numbers) from your simulation of the Resilient Ecosystem vs the Stressed Ecosystem in Activity C to revise your explanation.

Deliverable: Write a revised scientific explanation detailing how a combination of living (predation, invasive species) and nonliving (water, pollution) factors determine an ecosystem’s carrying capacity, and how those baseline factors dictate the ecosystem’s ability to recover from a moderate disturbance. Cite specific population numbers and biodiversity indices from Activity C as evidence. ___ _____ _______

Extension: Change the Ecosystem Scale from Regional Forest to Global Marine System while keeping the sliders the same. Run the model. How does the scale of the model relate to the final population numbers? (Use the concept of orders of magnitude).

Teacher Notes & Alignment

• NGSS Standard: HS-LS2-2: Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales.
• SEP: Using Mathematics and Computational Thinking. Students use the simulation’s mathematical model, charts, and numerical outputs (K, Population, Biodiversity Index) to support and revise their explanations of the phenomenon.
• DCI: LS2.A: Interdependent Relationships in Ecosystems (carrying capacities are limits governed by living/nonliving resources and challenges). LS2.C: Ecosystem Dynamics, Functioning, and Resilience (disturbances vs resilience).
• CCC: Scale, Proportion, and Quantity. Students relate models at different scales using the Ecosystem Scale dropdown and orders of magnitude.
• Evidence Statements Addressed:
  • 1.a.i-ii, 1.b.i-ii: Students identify components in the math representation (graph trends, population numbers) relevant to supporting/revising explanations about factors affecting biodiversity, recognizing that populations vary based on physical/biological dynamics, and that responses to small vs large changes affect populations differently.
  • 2.a: Students use mathematical representations (the 30-year model graph and data table) to identify changes over time in numbers of organisms.
  • 3.a.i-ii: Students analyze the math representations to identify important factors (water vs predation/pollution) determining biodiversity/population numbers, using it as evidence to support explanations for effects of living/nonliving factors.
  • 3.b: Students describe the representations in terms of supporting explanations for the effects of disturbances on an ecosystem’s capacity to return to its original status (resilience).
  • 4.a: Students revise their explanation (in Part 4) based on new evidence illustrating the effect of a disturbance within the ecosystem.

Sample Answers & Evaluation Rubric

• Part 3 - Q1 (Math Representation): Students should recognize that decreasing Water Availability strictly limits Estimated K (carrying capacity). Example: “When water decreased from 50% to 10%, K dropped drastically, meaning the resource limit restricts population growth.”
• Part 3 - Q2 (Comparing Factors): Students should observe that while High Pollution and High Predation both reduce the final population size, Pollution drives the Biodiversity Index down more severely because it degrades habitat quality, while predation primarily affects abundance.
• Part 4 - Revised Explanation (Elaborate/Evaluate):
  • Proficient Response: Cites the simulation data to explain that a healthy ecosystem (Resilient Ecosystem) with ample water (100%) and low stressors (10%) maintains a high carrying capacity. When the disturbance hits, the population drops but remains viable because the underlying limits are high. In contrast, the Stressed Ecosystem (low water, high pollution/predation) has a depressed carrying capacity; the disturbance drops the population below a sustainable threshold, causing total collapse. The data table numbers must be explicitly referenced as evidence.